The present invention relates generally to tractor and implement arrangements and more particularly to an improved hydraulic system for coordinating the action of a lift assist wheel on an integrally-mounted implement with the three-point hitch of the tractor.
A significant amount of attention has recently been directed towards improving the productivity and profitability of farming operations. As a result, tractors with increased capacities and implements having wider toolbars capable of supporting greater weights are now commonly available.
For agricultural operations which utilize tools such an cultivators or rotary hoes, it is common to integrally mount the implement toolbar to the three-point hitch of the tractor. During field operations, the weight of such an integrally-mounted implement is distributed through the tools to the ground and through the toolbar to the three-point hitch. However, when the tractor hitch and the integrally-mounted implement are elevated to permit transport of the implement, the weight is transferred totally to the rear of the tractor. Since tractors commonly available today are capable of pulling more than they can lift, integrally-mounted implements, if too wide and heavy will lighten the front of the tractor when they are lifted, possibly resulting in a complete loss of steering control.
It is well known to provide larger integral implements with hydraulically actuated lift assist wheels to reduce the weight transferred to the tractor during transport. See, for example, the Model 7100 Mounted John Deere Planter. In such arrangements, actuation of the rockshaft hydraulic cylinder utilized to elevate the lower draft links of the three-point hitch is coordinated with the actuation of the lift assist hydraulic cylinder to raise and support the implement for transport. Typically, such an arrangement provides for the lift assist cylinder to be supplied with hydraulic fluid through lines coupled with a remote hydraulic cylinder outlet on the tractor while the rockshaft cylinder is supplied with hydraulic fluid through a separate hydraulic circuit contained within the housing of the tractor. Since each cylinder is supplied through a separate hydraulic circuit, at least two cab-mounted control levers must be manipulated to operate the cylinders. Accordingly, the operator must coordinate the two levers and actuation of the cylinders when raising the three-point hitch and lift assist wheel to transport the implement. Occasionally, structural damage can occur to either the hitch or implement when the actuation of the cylinders is not coordinated and the three-point hitch is not elevated in near synchronization with the lift assist wheel.
A hydraulic circuit providing a single control lever to activate the tractor rockshaft cylinder and the implement lift assist cylinder has been provided when only single-acting lift assist cylinder capability is required. This ability is provided through special valving contained within a rockshaft piston cover available for John Deere Model 4030 and other similar tractors. The piston cover hydraulically connects the single-acting rockshaft cylinder in parallel with the lift assist cylinder. Accordingly, both cylinders are actuated when the rockshaft cylinder is pressurized and both cylinders are connected with the reservoir to permit them to be in a float configuration when the rockshaft hydraulic cylinder is not pressurized.
This hydraulic circuitry permits the operator to extend the lift assist cylinder and lower the wheel for transport. However, during field operations, the rockshaft cylinder must be connected with the reservoir to allow the three-point hitch and implement to float vertically in response to ground contour changes. During this time, the lift assist wheel, which cannot be elevated since the lift assist cylinder is single acting, will travel along the ground behind the implement and compact the soil. If cultivating operations utilizing tools such as rotary hoes are performed, the trailing lift assist wheel will compact the soil loosened by the tools. Accordingly, it would be desirable to be able to elevate the lift assist wheel during such field operations.
A double-acting hydraulic cylinder has been provided on integrally-mounted implements having trailing lift assist wheels, as for example, the John Deere Model 7100 Mounted Max-Emerge Planter. In this arrangement, the trailing lift assist wheel can be elevated during planting operations and lowered to assist during transport operations. However, the arrangement does not couple the lift assist cylinder with the rockshaft cylinder in a single hydraulic circuit utilizing a single control lever. Here also, the operator must synchronize two separate control levers to elevate the implement lift assist wheel and tractor three-point hitch for transport of the implement.
A further problem which arises during transport of integral implements having trailing lift assist wheels occurs due to the changing ground contours and the lateral separation between the lift assist wheel and the implement connection with the tractor. As the lift assist wheel passes over ground contours different from those contours beneath the rear wheels of the tractor, the hitch connection will be put under compression or tension. To avoid structural damage to the hitch and/or implement during transport, some provision must be made to the connection to permit the implement to rock fore-and-aft about a transverse horizontal axis to accommodate the changing ground contours.
The John Deere Model 7100 Mounted Max-Emerge Planter has provided a mast connection between the implement and a three-point hitch which permits the implement to rock fore-and-aft at its connection with the hitch. A single-acting hydraulic cylinder is coupled with the compression link of the three-point hitch and put into a float configuration during transport to enable the implement to rock. During field operations, the mast cylinder is pressurized to act as a rigid link and to enable the implement to float vertically over changing ground contours about the pivotal connection between the three-point hitch with the implement. While the 7100 Mounted Planter with its hydraulic mast has provided a double-acting lift assist cylinder coupled with the single-acting mast cylinder, it does not provide a hydraulic system that also enables the operator to activate the single-acting rockshaft cylinder in near synchronization with the activation of the lift assist cylinder to avoid structural damage to the hitch and implement and to also simplify the operation of the integrally-mounted implement utilizing lift assist wheels.